Atomistic Simulation Centre, Queen's University Belfast, Belfast BT7 1NN, Northern IrelandSchool of Chemistry, University of Bristol, Bristol BS2 1TS, United Kingdom.
J Chem Phys. 2011 Oct 21;135(15):154505. doi: 10.1063/1.3652897.
The role of dispersion or van de Waals (VDW) interactions in imidazolium-based room-temperature ionic liquids is studied within the framework of density functional theory, using a recently developed non-empirical functional [M. Dion, H. Rydberg, E. Schröder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004)], as efficiently implemented in the SIESTA code [G. Román-Pérez and J. M. Soler, Phys. Rev. Lett. 103, 096102 (2009)]. We present results for the equilibrium structure and lattice parameters of several crystalline phases, finding a general improvement with respect to both the local density (LDA) and the generalized gradient approximations (GGA). Similar to other systems characterized by VDW bonding, such as rare gas and benzene dimers as well as solid argon, equilibrium distances and volumes are consistently overestimated by ≈7%, compared to -11% within LDA and 11% within GGA. The intramolecular geometries are retained, while the intermolecular distances and orientations are significantly improved relative to LDA and GGA. The quality is superior to that achieved with tailor-made empirical VDW corrections ad hoc [M. G. Del Pópolo, C. Pinilla, and P. Ballone, J. Chem. Phys. 126, 144705 (2007)]. We also analyse the performance of an optimized version of this non-empirical functional, where the screening properties of the exchange have been tuned to reproduce high-level quantum chemical calculations [J. Klimes, D. Bowler, and A. Michaelides, J. Phys.: Condens. Matter 22, 074203 (2010)]. The results for solids are even better with volumes and geometries reproduced within 2% of experimental data. We provide some insight into the issue of polymorphism of [bmim][Cl] crystals, and we present results for the geometry and energetics of [bmim][Tf] and [mmim][Cl] neutral and charged clusters, which validate the use of empirical force fields.
在密度泛函理论的框架内，使用最近开发的非经验函数[M. Dion、H. Rydberg、E. Schröder、D. C. Langreth 和 B. I. Lundqvist，Phys. Rev. Lett. 92，246401（2004）]，研究了在咪唑基室温离子液体中分散或范德华（VDW）相互作用的作用。该函数已在 SIESTA 代码[G. Román-Pérez 和 J. M. Soler，Phys. Rev. Lett. 103，096102（2009）]中得到了有效实现。我们给出了几种晶相的平衡结构和晶格参数的结果，发现与局部密度（LDA）和广义梯度近似（GGA）相比，均有普遍的改进。与其他由 VDW 键合表征的系统（如稀有气体和苯二聚体以及固体氩）相似，平衡距离和体积的估计值比 LDA 中的-11%高出约 7%，而 GGA 中的则高出 11%。分子内几何形状得以保留，而分子间距离和取向则相对于 LDA 和 GGA 得到了显著改善。其质量优于通过定制的经验 VDW 修正[M. G. Del Pópolo、C. Pinilla 和 P. Ballone，J. Chem. Phys. 126，144705（2007）]实现的质量。我们还分析了这种非经验函数的优化版本的性能，其中交换的屏蔽特性已被调整以重现高水平的量子化学计算[J. Klimes、D. Bowler 和 A. Michaelides，J. Phys.：Condens. Matter 22，074203（2010）]。对于固体，其结果更好，体积和几何形状与实验数据的误差在 2%以内。我们深入探讨了[bmim][Cl]晶体多晶型性的问题，并提供了[bmim][Tf]和[mmim][Cl]中性和带电团簇的几何形状和能量学结果，验证了经验力场的使用。
